text:
Why do IFR reporting points have odd names?
I was checking out some flights on FlightAware and went onto the "Route" page for a flight and I saw these IFR Reporting Points with really odd names. Is there a regulatory reason why they have such names?

Page I snipped image from

I think answers here will be quite opinion-based.  All I know is that the names need to be pronounceable by humans for communication over radio, and there appears to be a 5 letter limit, which is why you get strange combos trying to make a pronounceable name out of 5 letters who knows how many unique times.

@RyanMortensen There will have to be at least a regulation for that though.

It's still not clear what's "odd" about these names. Although I have long wondered how it is decided when you can give a "cute" name to a waypoint.

Names are chosen for their mnemonic value and often relate to local landmarks and attractions. For example there is a reporting point near Green Bay Wisconsin called LMMBO for Lambeau Field where the Packers play.

Check out the FRDMM 3 and TRUPS 3 arrivals to KDCA. They spell out sentences

ITAWT-ITAWA-PUDYE-TATT ... IDEED

It seems to be about 9,000 5-letter words in English (anything else will seems odd to an English person). If ICAO removes entries that are confusing (e.g. THREE, LEVEL or SPEED) or inappropriate in any language (MORON, ITLER, BURNE), the list will be quickly reduced. So it's not surprising to see COSMC, ZORBO, or even MEGSS. Also not all fixes are to be used on ATC communication, some are for procedure design only.


text:
What is the difference between a barrel roll and an aileron roll?
I was going through social media and I came across this GIF image that showed a plane doing some sort of roll.

It was labeled "Barrel Roll" but in the comments to the post, someone said that it was an "Aileron Roll". What is the difference between a barrel roll and an aileron roll?

Related: http://aviation.stackexchange.com/questions/22793/what-is-the-concept-behind-being-able-to-continuously-pour-iced-tea-while-rollin/22804?s=13|0.1711#22804

anyone who hasn't seen Bob Hoover pouring tea while doing a roll needs to watch this: https://www.youtube.com/watch?v=yO8GyU8asEI

That is one very cool and inspirational video - and not just the pouring-water part.

The difference between an aileron roll and a barrel roll is that an aileron roll's centre of rotation is very close to or on the aircraft. A barrel roll has its centre of rotation around a point further away from the aircraft itself.
The difference can be appreciated in this image:

Image Source You can find out about the difference in feeling that these two manoeuvres have.
Having stated these things, the manoeuvre shown in the GIF is certainly an aileron roll.

I noticed in that GIF that at certain points the roll seemed to slow. Is this inherent to an Aileron roll or was that just some quirks of the pilot?

@DavidGrinberg I see slowing down only at the very end of the video (perhaps also the end of the maneuver). Of course the apparent motion of the wingtips is faster when they are going up or down from the camera's point of view than when they are going directly toward or away from the camera, but that's only apparent motion, not the actual speed of the rotation.

@DavidGrinberg: In an aileron roll, the rate of roll is fully controllable by the pilot. With the right aircraft the pilot can literally stop the roll at any point and maintain the aircraft's orientation. There is a precision variant of the aileron roll called the "four point roll" where the pilot rolls 90 degrees then pause then another 90 degrees then pause etc.

In a barrel roll, the aircraft rotates both in its longitudinal and lateral axes, while in case of aileron roll, the rotation is only about the longitudinal axis.

A barrel roll, image from flightsimbooks.com
If properly executed, there is no change in alttitude in case of an aileron roll, while during barrel roll, the aircraft follows a helical path.

An aileron roll, image from globalsecurity.org
In short, think like this- in a barrel roll, the aircraft goes along the surface of the barrel, while in an aileron roll, the aircraft corkscrews around inside a barrel, with the wingtips grazing the barrel surface.

So Peppy got it wrong?

I heard that the definition of a barrel roll was that the aircraft was always under positive Gs. Is this accurate?

@Steve Yeah, the definition I've always heard is that a barrel roll (when executed properly) is a constant +1 g downwards manuver (meaning even large planes not capable of high g forces could accomplish one), whereas the aileron roll has an additional acceleration.

@DC177E You must have more than +1G in the pullup between point 3 and 4 in aeroalias diagram.

i posted this above, but you can tell its a +G maneuver bc its possible to pour a glass of tea throughout the roll https://www.youtube.com/watch?v=yO8GyU8asEI

Edit needed : "alttitude" - is that a new term for altitude AND attitude?  :)

There is no precise, universally accepted definition of "aileron roll".  If the rotation were purely about the aircraft's longitudinal axis, then any positive angle-of-attack existing at the start of the maneuver would be converted to pure sideslip after 90 degrees of roll, and to a negative angle-of-attack after 180 degrees of roll, at least in the simple case where the wings are attached to the fuselage at zero incidence as measured relative to the longitudinal axis.  Such a roll could be done with the aircraft following a nearly linear trajectory.  Yet an "aileron roll" is usually described as a maneuver than can be carried out with light positive G all the way around, and no sideslip.  This must involve somewhat of an arcing trajectory if the aircraft is to finish the maneuver at the same altitude it starts at, although the arc may be hard to detect in the case of a fast jet.
In short, it is not universally agreed-upon whether the term "aileron roll" should be applied to a maneuver that involves positive G, or negative G, at the point where the aircraft is inverted. The positive-G concept is the more common one.
Still, the most common conception of an aileron roll involves rotation that is MOSTLY around the aircraft's longitudinal axis and involves relatively little change in heading or pitch attitude, while a barrel roll is usually described as a maneuver involving a great deal of heading change, often 90 degrees or nearly so, as well as a great deal of change in pitch attitude.
All things considered, it's complicated.  Is the aircraft rolling around its longitudinal axis, or the airspeed vector, or neither?  Is the orientation of the aircraft's longitudinal axis staying fixed in space, or is the orientation of the airspeed vector staying fixed in space, or neither?  Is flight path linear or arcing?  If we had an "x-wing" plane with a set of vertical wings as well as horizontal wings, all with symmetrical airfoils and zero incidence, then starting from an initial slightly nose- high attitude, we could roll around the aircraft's longitudinal axis all day long with very little disturbance to the flight path.  We wouldn't be able to pour water into a cup on top of the dash though.  Would this be an "aileron roll"?  It's hard to argue that it wouldn't be, but it's not what we usually envision when we speak of an "aileron roll".

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text:
What is the fatigue life of a fuselage based on?
The fatigue life of the fuselage is based on the number of what? Pressurization cycles?

Related

Most (large) aircraft life times are measured in cycles.

"Aircraft lifespan is established by the manufacturer," explains the
  Federal Aviation Administration's John Petrakis, "and is usually based
  on takeoff and landing cycles. The fuselage is most susceptible to
  fatigue, but the wings are too, especially on short hauls where an
  aircraft goes through pressurization cycles every day." Aircraft used
  on longer flights experience fewer pressurization cycles, and can last
  more than 20 years. "There are 747s out there that are 25 or 30 years
  old," says Petrakis.

But that only applies to pressurized aircraft, there are large planes that are un-pressurized and their life is generally measured in flight hours. However most large aircraft like say the DC-3 don't have any imposed hourly limit on the fuselage but other parts may be hour/life limited.

The safe/fatigue life of a structure is the number of events
during which there is a low probability that the
strength will degrade below its design ultimate
value due to fatigue cracking. The events may
be flights, flight hours, landings, pressure cycles
or engine cycles.
Safe life may be determined by using a similar
structure (usually called a fatigue specimen)
which is tested to establish the minimum number
of events which should elapse before a major
structural failure occurs. For example the safe
life of the Cessna 310 wings is 19,190 flying
hours.

wings and fuselage operate under the same system when it comes to fatigue life and how its calculated

Often based on G pulled as well.  Some aircraft have G meters in the fuselage and a fatigue index calculated from the G counts.

"The events may be flights, flight hours, landings, pressure cycles or engine cycles." The text covers all structures and just gives an example of wings..

Don't forget the fuselage of most semi monocoque aircraft are made up of multiple structure each of which will have it;s own safe life or may not have a safe life at all, using instead single or multiple load paths or failsafe structures which negate the idea of safe life.

@Simon Yup, helps with those troublesome heavy landings as well ;-)

Metal fatigue is measured in cycles, indeed, but not necessarily in flight cycles. However landing cycles are a good measure of fatigue life, as can be seen in an iron bird set-up at an aircraft manufacturer. Complete cycles are simulated:

A row of actuators are connected to the wing. They start with a bit of rumbling downwards pressure, simulating taxiing.
Then more pronounced rumbling, followed by a sharp wing up deflection, simulating take-off. You can hear the structure groan when this occurs.
A hissing sound gets more and more pronounced: the fuselage is being pumped up like a beach ball. More groaning, it's literally a strain.
When pressure differential is at maximum cruise altitude, we're descending again, after a while we can hear the air escape and the fuselage settle in.
SLAM! A sudden sharp downwards kick on the wing, we've touched down.
And back to the beginning.

These birds make hundreds of flights a day, simulating all that happens during a flight. The wing experiences lots of smaller cycles during taxiing, and two huge ones during TO and landing. It is the number and the magnitude of these cycles that determine fatigue life.
Your question was specifically about fuselages, they are subject to taxiing cycles and pressure increase/decreas cycles. So if we take a decent cross section of runway surfaces and average taxi time, we can tie the taxi cycles to a flight cycle, and continue flying the iron bird again and again...

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text:
Are any Boeing 720s still flying?
A Boeing 720 looked like a 707 but was the size of a 737. I flew in one in 1961. I did not travel regularly until 1970 but I do not remember ever seeing a 720 again. Was it intended to have limited production? Are there any 720's still flying?

From a distance the B-720 looked exactly like a B-320. Both aircraft were powered by four P&W JT-3B engines; however, the B-720 engines were de-rated to 17,000 lbs. of thrust from  the 18,000 lbs. for the B-320. Additionally, the MTOW of the B-720 was 235,000 lbs. vs. 336,000 lbs for the B-320.  The B-720 was a real "hot rod" when it came to performance.

The last one I saw was parked on the ramp at Shannon in Ireland, if anyone's looking to take pictures.

'the size of a 737' threw me a bit, so I looked at the Wiki article. 'A 720 is a slightly shortened 707' would be a more accurate description IMO.

According to Wikipedia, no. The last one was retired in 2010.


text:
What is the difference between redundancy and fault tolerance?
What is the difference between redundancy and fault tolerance in the context of aviation ?

Redundancy is when there are multiple ways of doing the same thing; quite possibly by having multiple gadgets, or ways of interconnecting gadgets, that can perform the same function with the same or at least very similar fidelity even if a non-zero number of them fails. One likely effect of this is that there is no single point the failure of which will cause the failure of the entire system (no "single point of failure").
Fault tolerance is when the overall system can tolerate the failure of a component without going into a dangerous state, but it won't necessarily maintain the safe state by having full functionality or fidelity. The system may operate in a degraded state, but it won't immediately be in a dangerous state.
Redundancy can be a way of providing fault tolerance in the larger system, but redundancy on its own does not guarantee fault tolerance, particularly against all kinds of faults. It's only redundancy if each separate way of accomplishing a goal can function without the other ways of accomplishing the same goal. Fault tolerance is a result; redundancy is one way of achieving that result.
For example, there are two basic ways by which you can cause an airplane to assume a new heading; either by using the ailerons to bank, or by using the rudder to skid. Normally these are used together in a coordinated turn, but if you're really in a pinch, either one can be used to turn (but watch that stall speed). This is one crude example of fault tolerance, since either the ailerons or the rudder can fail and you are still able to make a turn (other effects of the failure, or other effects from the cause of the failure, notwithstanding). — Redundancy, on the other hand, would be more like if you had multiple independent sets of rudders and ailerons, each with its own, independent control system.
Commercial aircraft often have two or three of each flight-critical instrument; one for each (of two) pilot, and one backup instrument. For example, each pilot will have their own attitude indicator ("artificial horizon"), and they will have a shared instrument that can be used to, for example, determine which instrument is faulty if there is a disagreement between the two main instruments. This is an example of redundancy, because if designed right, any one of them can be used fully independently of the others to determine the aircraft's current attitude; the ability of the instrument to carry out the intended function at full fidelity does not depend on the others functioning properly, and there is hopefully no single failure which will cause two or three to fail in the same way, or at all.
An example where having redundancy doesn't necessarily provide fault tolerance can be having multiple hydraulic systems to control deflection of control surfaces. If all hydraulic systems are routed through a single location, and that location is damaged, there exists a possibility that you will lose all hydraulic systems at once due to that single failure. Therefore the hydraulic system is redundant but not necessarily fault tolerant.

perfect! thank you

Or redundancy is when there is no single point of failure.

@mins I meant for that to be covered by what I wrote, but I have now spelled it out.

@aCVn: Airliners have a third way of controlling heading--differential engine thrust.  That can sometimes provide adequate control to keep the airplane aloft even if all hydraulic control systems fail.  The level of control offered by engine thrust alone may not be sufficient to safely land the plane, but may be sufficient to make the landing survivable for at least some of the occupants.

I'm sure Capt. Haynes can give a pretty thorough dissertation on the benefits of redundancy and why it's still needed to cover a-billion-to-one odds. And I think Capt. Fitch can speak a bit about controlling an aircraft with just engines. https://en.wikipedia.org/wiki/United_Airlines_Flight_232  <<< That accident has so many good lessons. It should be required study for EVERY pilot.

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text:
Why is the speedbrakes rate of retraction 25 seconds when used at speeds greater than 315 knots/.75 Mach on the A320?
While I was routinely reading the FCOM normal procedures I came across a note with regard to the speedbrakes retraction time going up to 25 seconds when we use them at speeds at or over 315 knots / .75 Mach.
Why is this ?

Presumably the speedbrakes cause a significant change in flight characteristics, and you want that to happen gradually at higher speeds.

@DJClayworth Yes, they cause quite a change in pitch moment balance as far as I know. Not sure whether that’s the only reason, though.

Other possibilities are that there is some kind of noise that scares ppl if they are retracted quickly, or there is a ballooning effect from having significant lift restored at that high a speed that creates an unpleasant G load.  When we used flight spoilers on the CRJs you were supposed to retract them in steps.  You'd have to get lucky and find someone on here that is associated with AB engineering to get a definitive answer I expect.

Suggest you ask your flight ops management about the process for sending questions to Airbus's Liaison Pilot organization (they may call it something else). LPs are the primary interface between the operator flight ops community and AB's engineering organization, and one of their jobs is answering these sorts of questions submitted by flight crews.

@JohnK I have tried it in the past I got a response that these are design features mostly. It never got raised with Airbus after that. Whenever I have asked a very technically oriented question I got this reply

note that "25 seconds" is not a "rate of retraction", it is a time. a rate of retraction would be, for example  "1°/sec"

Please read the entire answer to understand the matter even if the answer goes a bit beyond the question.
On the A320 wings you have panels that may open upward and that could be used to fulfill 3 different functions: ground spoilers, speed brakes, roll spoilers.
The outer panels are used in addition to the ailerons for roll function, that is helping the ailerons only on one of the wing according to the turn direction.
The central panels are used in flight for the speed brake function as follows: when the pilot order is beyond a limit the Fly By Wire will provide protections because an excessive drag might damage the wing structure, so the higher the speed the lower will be their maximum angle of deployment and their speed of deployment even if the pilot gives a full order of deployment.
The drag produced by the air brakes causes a mechanical torque on the wings roots, a sudden removal of the drag would be similar to a stress cycle, therefore deployment and retraction are managed to protect the wing structure.  Any pitching effect of these surfaces in flight is automatically compensated by the FBW through the elevators.
At landing the ground spoilers function is as follows; all the surfaces are deployed fully if the function is armed.


text:
What is that missing instrument on a Beechcraft 1900C?
(Full image) Beechcraft 1900C.
I cannot find the name of the missing instrument even in the manuals.

Originally there was no instrument at this place, except for UE series with an electrically driven artificial horizon, where there was a fast erect pushbutton/indicator for the copilot gyro.
According to Wikipedia, UD series is for the military model and UE series is for 1900D, so I assume UC series is for 1900C model. Instrument panel for series UA/UB/UC:

Instrument panel from training manual, models UA/UB/UC (source)
Anything visible here has been added after the aircraft left the plant, when the panel was retrofitted. When browsing pictures of this cockpit online, we can see various additions:

Sources: Left, center, right
Looking at details of your image, we can see there was likely a sticker and a button associated with the instrument. This could fit with a battery temperature indicator and its test button:

Source: Right
This configuration was actually found on F-GPYY. Comparison:

Source: Right
Full cockpit of F-GPYY when it was an aircraft of the now defunct French Air Littoral operator:

Photo by Thierry Izzi, source

It's a missing instrument because it's not part of the standard avionics of the 1900C model but part of the Beechcraft's 1900D aircraft avionics.
If you take a look at pages 0 and 1 of 31-10-00-01 (chapter 31, section 10, unit 00, figure 01) of the Beechcraft 1900D aircraft's IPC (Illustrated Parts Catalog),¹ you'll notice that the hole featured on the picture that you provided is precisely the item 100 (Part Number 101-380031-3), which is the Copilot's Turn and Slip Electric Indicator (technical nomenclature INDICATOR-COPILOT TURN AND SLIP, ELECTRIC).
Looks like this 1900C aircraft is using a 1900D aircraft panel plate/harness but it doesn't have all the 1900D's indicators, hence the missing item 100.

Footnotes:
¹ Pages 6 and 7 of the PDF file.

That’s no turn and slip indicator

I flew the 1900D. We had 20 of them in the fleet but there wasn’t a gauge or hole there.

Perhaps the difference is because 1900C and 1900D are different?

For sure they are. I was referring to Yuri’s comment about the photo looking like that 1900C using 1900D panels. Between operators there can be various differences in the avionics package, and ultimately I don’t think there’s anyway for anyone to know simply from the photo what used to be in that spot. There should be a supplement in that aircrafts technical/operating manuals that specifies what instruments/gauges would have been installed.


text:
How far does an A320 travel horizontally while climbing to / descending from cruise altitude?
I am trying to determine how far an A319, A320, and A321 travel horizontally while climbing to / descending from cruise altitude? Would anybody be able to help me calculate this?

This question is unanswerable due to angle of attack, airspeed, air-brakes, pilot technique, throttle settings, gross weight, density altitude, etc.

@jwzumwalt… and yet it already has an answer and that answer already has 7 upvotes.

Are you asking for V/S in open climb or open descend mode?


text:
What is the main materials of the windshield? And how do they function in bird strike?
I would like to know what the latest materials used for civil and military aircraft windshields are.
And I wonder if the materials are advantageous in the event of a birdstrike.

Searching for "airplane windshield material" found me this: https://aviation.stackexchange.com/questions/44412/what-materials-are-used-for-aircraft-windshields

This question is too vague and subjective to be answered. There are vast differences in the construction, size, thickness, lamination, and angles of windshields.

Here is an example of the latest and greatest.
http://www.ppgaerospace.com/getmedia/926cb26f-e047-477d-b604-62d079f494bc/B787_TD_FINAL.pdf.aspx?ext=.pdf
You will notice that instead of multiple glass laminations separated by plastic interlayers of traditional aircraft windshields, the 787's windshields are basically two thick layers of acrylic plastic (plexiglas) as the main structural element, with interlayers to separate them and just a single outer layer is high strength glass.   This would provide superior birdstrike resistance while the glass outer layer maintains a hard outer surface that won't scratch easily.


text:
What is this old biplane?
Can anyone identify this aeroplane?
Location is Cordoba, Argentina.

This is a tricky one. If you could say what the source is if possible that might help. (Cordoba might be Spain, or might be Argentina, for instance.)

Hi and welcome back! Please take a couple of minutes to take the [tour] and read through the [help] so you can learn how to make the most of the various SE sites! Thanks.

Maybe a sopwith pup

The aircraft is one of many (5 or 6) SAML-Aviatik type "S" and type "A" Italians that flew in Argentina in the '20s. All were for civilian use. Most had Colombo or FIAT engines in line, but the one in the photo (type "A") was the only with a rotary engine (Le Rhone?) that flew in Argentina. It belonged to the Italian pilot Renato Balleri, who together with the American Henry Johnson made public shows of flights, acrobatics, parachute jumping and flight baptisms throughout the country.
Henry Johnson died in an accident one of those events, in the city of Quilmes, in 1934.
The images are of this same plane in the province of San Luis.

Here an Italian SAML-Aviatik A.2...

Interesting story, and the wing shows good agreement with the photo in the question. But the engine cowling looks quite different and also the very pronounced step on the fuselage side is missing in the original picture. The engine in question clearly is a rotary one, so again one indication for the SAML-Aviatik. But questions remain.

The A.2 looks like a good match, the rudder in particular.

It Looks like avro 504K,see this picture

Note that in the upper photo in your answer the top wing appears to have dihedral, although without more information we could not rule out forward sweep which would create the same appearance from that camera angle.  Note that the upper wing of the biplane in the question appears to have anhedral, which is almost certainly due actually entirely or mainly to the fact that the wing is swept aft, which creates the same appearance from that camera angle.  That's a pretty fundamental difference in geometry-- they cannot be the same type of plane.

Also consider fore-and-aft spacing of wing stuts which is very small in Avro 504, fin/ rudder shape, strong positive stagger in Avro 504 and little to none in airplane in question, and more.  Also note that the wing struts on the 504 are raked forward relative to the fuselage-connected struts ("cabane" struts).

See also the triangular geometry of some the "cabane" struts in the question photo.

Bravo  for this attentive look!

Looks a lot like an Anatra D-Series. Note the scalloped trailing edge and the chunky wing struts. These were Russian built aircraft used for reconnaissance during WWI.

uhm, but in OP's photo there is no cutout for the pilot in the trailing edge of the upper wing. also, the engine shape looks different.

The landng gear looks further forward than the OP's aircraft

See the face....not the same


text:
How can a Cessna cut the wing of a Boeing?
I read days before about the collision of the flight PSA Flight 182 on September 25, 1978. I was wondering how is it possible that a Cessna 172 can CUT Boeing's 727-214 wing. There is a video with the moment: video.
Is there an explanation of how this can happen scientifically?

An airliner wing is built to be as light as possible. Its strength is calculated to withstand the stresses of flying, i.e. lift equally distributed over the wing, bird strikes on the leading edge.
The wing consists of one or more spars from the fuselage to the wingtip, ribs perpendicular to the spars and skin panels. All of these are made from thin aluminium: the spars (the main loadbearing structure) are a few mm thick outside the landing gear and engines.
Fire a one-ton object into the wing at a few hundred km/h and you can do a lot of damage. Even if that object is another aircraft with similar construction.
The damage gets worse if the wing hits the Cessna's engine block, but the accident descriptions I've seen don't say if that was the case.
Don't assume the animation is accurate. The Cessna won't slice cleanly through the wing, there would have been a collision in which both structures are crumpled and roughly torn apart.

Is it possible that Cessna's flag would be stronger than Boeing's because of the much smaller size and thus more densely than Boeing's?

@avionerman The Cessna would be subjected to far lesser loads under normal operation. To a first order approximation, the wings need to carry the maximum takeoff weight of the airplane, plus a margin for maneuvering and safety. That's going to be less for a small airplane than a large one.

@a CVn So if we could give an example, the Boeing because of the long wings was like a paper and the Cessna because of its small wings (and with less weight) was like a pen and that is why it "pierce" it so easily. Is that right?

Compare to a Coke can. You can easily dent a can from its side, but you can stand on top of that same can without it collapsing.

@avionerman Look up "wing loading".

Thank you both for the answers. I had no idea what is wing loading. I am glad that now I get it. Once more thanks for your time both.

PSA Flight 182 hit the rear of the Cessna, striking the vertical components, the rudder and vertical stabilizer. It was not a wing-to-wing impact.

Large objects are fragile. Pretty much any two airplane-sized objects, when colliding at airplane-like speeds, will both be damaged by the collision.
The reason for this is the square–cube law. As you increase the size of an object, its strength increases more slowly than its mass increases. So as a result, small objects tend to be very strong, and large objects tend to be very weak. That's why you can hurl a toy car into a stone wall at 10 mph and it will be completely undamaged, whereas if you run a real car into a stone wall at the same speed, it'll be damaged severely.
In a comment, you compare the two airplanes to a sheet of paper and a pen. I don't think this is a good analogy, since a pen is much stronger (relative to its mass) than an airplane is. A better analogy would be to imagine both airplanes as raw eggs.

Thank you very much for your answer. I really like your example :)


text:
How, exactly, did US1549 land on the Hudson?
A comment by @AsheeshR says:

The Hudson River Landing was due to a combination of piloting skill and an autopilot system that was engaged right till impact and kept the plane in a controlled descent within a safe flight envelope.

It was an Airbus aircraft, so the autopilot has priority over pilot input, but how exactly did the autopilot play a role in getting them down safely?
What exact procedures did Sully and the crew follow when landing? Was there anything in addition to standard ditching procedures, that might have contributed to them landing in one piece?

I believe Airbus have a "ditching" switch in the cockpit that seals the hull.

@RedGrittyBrick You're right, but it wasn't pressed on this particular flight.

@flyingfisch See http://youtu.be/Zzjbubs59Ks?t=23m45s - it was at the end of the checklist, which they didn't have time to complete.

@DannyBeckett Oh, wow, that's awesome

@flyingfisch The ditch switch is meant to close openings in the fuselage through which water would make ingress, and slow flooding of the fuselage; however, it wouldn't have done much good in this situation, because the forces of impact ripped holes in the hull anyway.

I have no idea if this was deliberate, skill, luck or accident and I can find no reference; If you watch the video, it seems to me that he touched down with low speed but not so low that the pitch angle would be such that the tail would dig in and slap the fuselage down or shear it off.   Looks like the tail dragged just enough to bleed off the speed and settle the fuselage down. I saw an interview with an experienced SLF who said that the forces when the fuselage leveled were not that much higher than during a firm arrival such as might be experience in a 737 in bumpy conditions.

Probably the most important factor was that the captain started preparations for a forced landing immediately when the engines flamed out. Compare the Dana Air MD83 crash at Lagos on Jun 3rd 2012. There is no final report yet, but the preliminary one suggests the crew failed to try and select emergency landing spot.

"the plane inherently has more control anyway" What? It seems like you're making that up...

@NickT So click the link then?

@DannyBeckett I did, I don't see what you're referring to at all.  That entire QA seems rife with subjectivity.

@NickT In a Boeing, ultimate control is left to the pilot, and the aircraft will not override the pilots' inputs. In Airbus aircraft, the opposite is true. Ultimate control rests with the autopilot, which the pilots cannot override.

Japan Airlines Flight 2 did an inadvertent water landing in 1968. Photo

just jumping in (again) against the 'autopilot overrides pilot on Airbus' story that is going on arround. It's like saying Traction Control overrides a driver's inputs (it does, for better performance). And you can switch it off (same in an Airbus). Pilot is always in full control (and in charge).  A320 type rated

@DannyBeckett you are misinterpreting the FBW laws/protections with the Autopilot. AP is either on or off. There is no manual flight when AP is on  and no AP will override anything durring manual flying. It's like, say, the difference between Cruise Control versus Traction Control (or Rev Limiter) on the car. One is protecting, other is driving(if cruise control was driving.. I dunno)

@Radu094 I'm referring to Airbus having alternate law, per http://aviation.stackexchange.com/a/11830/97

@DannyBeckett thanks!  I've invaded that thread with comments aswell :-)

The NTSB report is a great resource when looking for information about an incident like this.
There is an Engine Dual Failure Checklist discussed starting in section 1.17.1.2 of the report. This includes steps to attempt restarting the engines, and further steps depending on whether or not the engines can be started, and finally steps to help prepare for a forced landing. Pilots train on engine failures regularly, so they are already familiar with the procedures. The report discusses how their actions compared to what the checklists say. Since the incident occurred at such a low altitude right after takeoff, they didn't have time to complete all of the steps. They did what they had time for, and had to make quick decisions about what their options were.
The report also discusses in section 1.17.3.2 the ditching training the pilots received. There was guidance in the manual, but no specific scenarios included in their simulator training.
The autopilot is great for use in normal situations. However, as soon as anything is going wrong, the pilot should take control of the plane. You do not want to take time to figure out "what's it doing now" in a difficult situation. So in this situation, the autopilot probably disconnected when the engines went out, or was manually disconnected by the pilots.
Section 1.6.3 talks about the flight envelope protections. I believe these protections are what you are referring to when you say that the autopilot has more control. They are designed to protect the plane from stalling or otherwise exiting controlled flight. Because the pilot was able to start the APU to provide electrical power, the plane remained in the "normal law" mode where these protections were available. This limits the control the pilot has in order to protect the plane, in the sense that the plane will override pilot inputs to avoid dangerous situations.
Section 2.7.2 discusses the impact of these protections in this case.

The airplane’s airspeed in the last 150 feet of the descent was low
  enough to activate the alpha-protection mode of the airplane’s
  fly-by-wire envelope protection features...
Because of these features, the airplane could not reach the maximum
  AOA attainable in pitch normal law for the airplane weight and
  configuration; however, the airplane did provide maximum performance
  for the weight and configuration at that time...
The flight envelope protections allowed the captain to pull full aft
  on the sidestick without the risk of stalling the airplane.

An interesting point in the report is that Airbus certified the plane to be able to land on the water intact under certain conditions. Here is how the actual conditions compared to the certified conditions.
Section 1.6.7

The report mentions that it would be extremely difficult to meet all of these requirements in an airplane with no power. The values that are higher, notably the mass and descent rate, are factors in the damage the airplane received.

As @Lnafziger mentioned, the amount of "nannying" that an Airbus does compared to a Boeing is debated among pilots. Airbus, for example, won't let you jerk the controls to the point of possibly losing control or bending metal. Boeing will let you, so that if you come out of a cloud and see you're going to collide with another plane in 3 seconds, you can pop a few rivets but avoid a mid-air. Boeing also gives a lot more tactile feedback on the controls and involves the pilot more heavily, which can have its advantages (the downside is more routine workload).

Examples of how the Airbus system works well are in this ditching case (pilot wants best nose up performance, doesn't need to judge manually) and the incident here, where the plane prevented an inadvertent nose down from damaging the plane.

The autopilot and autothrottle were both disengaged and, thanks to the quick thinking of the Pilot Flying to activate the Auxiliary Power Unit (APU), the aircraft stayed in Normal Law. This assisted when ditching due to the transition at 50ft to Flare Mode that causes a pitch down attitude allowing the pilot to pull back with a constant pressure on his side stick to cause the plane to flare for landing.

We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

You should improve your answer by adding reeferences and explaninig what your answer add to the rest of the other answers

"technically" the best answer so far, and the only one to correctly point out that A/P was off. Guys, you cannot fly manually with  A/P on. People all over this page have mistaken FBW protections and laws with the Autopilot

There is not much training for situations like that because they are very rare and the simulators cannot teach accurately what to expect when a plane touches down on water.
The captain in this situation got almost everything right for a water landing, as he kept the nose up and wings level, he let the tail hit the water first slowing the plane down enough so it survived the impact.
I'm not sure autopilot played much role in this if any, because there was no runway length and reverse thrust to concider.

I disagree that there's "not much training for situations like this" - ditching is definitely a commonly practised procedure.

From the Air Crash Investigation episode on this accident @ about 11:25 -- "Investigators Soon Learned that none of the Major Airlines Teach Pilots how to Land On Water. Training for Ditching in water is very difficult, we don't have the models to accurately simulate what a plane will do when it touches down on water, Given the rarity of this type of event it will be difficult to justify training for training pilots for this type of event"

Thanks for that! It sounds like I stand corrected. Does anyone else know about this?

Your thinking about "Ditching" and you are correct, there are procedures for that, and for "Water Ditching" their is some standard procedures pilots learn to follow. There must some Knowledge as to what to do in  situations like that and from historical experience. But Learning how to do that its very difficult.

FWIW, in my 10 years of taking 747 simulator check rides, ditching was regularly practiced.
There was a checklist for ditching. It included recommended touchdown configuration, speed, pitch attitude, and admonitions for landing parallel to the swells if possible. There was a lot of work for the flight engineer (3 man cockpit), a lot of setup including making sure the outflow valves were closed and the like.
As I remember, the recommended pitch attitude for the 747 was 5 degrees nose up. I can't remember the recommended flap setting.

With which airline do you fly? -- The FAA does not require commercial pilots to train to ditch but airline cabin personnel must train on the evacuation process. In addition, the FAA implemented rules under which circumstances (kind of operator, number of passengers, weight, route) an aircraft has to carry emergency equipment including floating devices such as life jackets and life rafts. --- Source -- http://en.wikipedia.org/wiki/Water_landing#Commercial_aircraft


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What causes the sudden spool-up sound from an F-16 when enabling afterburner?
What causes the sudden spool-up sound from an F-16 when enabling afterburner?
I've included a video to make it clear what sound I'm referring to:

at 1:16, I assume the pilot engages afterburner (again), and there is a sudden spool-up sound associated with this.
Am I even correct in assuming this is what's happening? I don't understand what this sound is though, it doesn't seem to appear consistently. Throughout the video, it appears the pilot engages afterburner and turns it off multiple times, but the sound only appears once.
Bonus question: What is the purpose of running the engine like this, and how is the F-16 attached to the ground?

That guy walking under the plane had really better hope the cable is strong enough...


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Are there any missile systems as of 2019 capable of shooting down aircraft in excess of mach 6?
Are there any missile systems, ground based, or air to air, as of 2019 that are capable of shooting down aircraft in excess of mach 6, such as the X-15?
For simplicity I'm ignoring the fact that the X-15 may be considered a spacecraft or "space plane".

Asking for a friend, of course.

@DavidRicherby a friend in the Iranian ministry of defense procurement office?

@jwenting Not necessarily. It could be a friend who owns a very fast plane.

The Russian S-400 SAM System is claimed to be capable of speeds in excess of Mach 12 and ranges of 400 km (250 miles).  It can, in theory successfully engage and defeat hypersonic targets, albeit with a much smaller lethal envelope than against conventional aircraft or missiles


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What happens in an F-16 once the aircraft exeeds its service ceiling?
What exactly is the sequence of events that would unfold as an F-16 attempts to exceed its service ceiling? The scenario is simply full afterburner and attempting to simply climb higher and higher (at arbitrary/ideal angle of climb) until something prevents that.
I'm curious mostly as how this relates to flight simulators which simulate the F-16, if this can be improved, and if flight simulators already accurately depict what actually would happen in reality.
I'm aware of What determines the maximum altitude a plane can reach? but this is too general and doesn't answer for any specific aircraft. I think it would be both interesting and useful to have a specific aircraft as an example.
What fails first? Engine, or lift? Both more or less simultaneously?
1: What happens to the engine? Will it see an increase in temperature? Will it flame out?
2: What happens to the control surfaces? The airframe? I would imagine nothing, certainly no shaking as portrayed in certain TV series involving aircraft.
3: What happens to the instrumentation? Master caution? Relating to 1, engine warning light? FTIT?
4: Life support, can the life support cope with this?

The F-15C has a service ceiling of 65,000 feet, but it also holds an altitude record of nearly 103,000 feet.

@Ron, the record-breaking Streak Eagle is not the same aircraft as F-15C (F-15A in fact, and substantially modified). And neither hold the current record. Altitude still belongs to (a version of) MiG-25 (~123K feet). That one actually lost both engines at the apex.

It's not clear whether you are talking about sustained theoretical ceiling, or the highest achievable dynamic ceiling. Either way, this is not a "simply full afterburner" scenario. I don't know F-16 enough to answer, but only in the second case your question becomes interesting: there you indeed may hit the limits of engine (flame-out) and life support, in addition to lift (which by definition will be exceeded: ideally, the aircraft will have zero speed at the apex; in practice it can be <50 kt IAS).

What makes you think that the F-16 has a specified service ceiling? I'm not sure you understand what service ceiling is. Service ceiling is a  term with a meaning dependent on specific certification criteria. What is the prescribed value by which the service ceiling would be defined for an F-16?

What happens in real life is not completely different from what happens in hard sims; the ceiling is not a hard line, but an equilibrium point defined by performance limits.
You can zoom climb well above the static ceiling in a ballistic arc. The static ceiling is simply the point above which the aircraft won't be able to produce enough thrust and lift to sustain that altitude. You'll start losing velocity, and as you do so, also start losing altitude. Nothing fails outright. You just don't have enough energy to climb or even stay level.
The engine will work (but flameout is possible).
The control surfaces will work (but not very well).
The instrumentation will work and there's no master caution for simply exceeding the envelope.
Life support systems will work just fine.
You'll lose altitude whatever you do, however.

You won't necessarily lose altitude, service ceiling is defined as to which you can't climb at more than 100ft/min. What does happen is you get closer and closer to the coffin corner, which is the aerodynamic ceiling.

@RonBeyer coffin corner isn't really relevant to a supersonic aircraft, there are somewhat analogous limits but the behavior is different

You seem to assume that one starts off the service celing and just attempts to climb further. This is not how the highest altitude is achieved. But even if we do that, it's a big question whether we run out of thrust or lift first. Different aircraft have it differently, and I can only guess about F-16. (My guess is lift, but supersonic arcraft often have two local altitude maxima on their envelope).

...If we assume ballistic ('zoom') climb to the dynamic ceiling (it's not clear whether the OP asked about it), then things can be very complicated, and I will argue that most sims will likely have it wrong (particularly with respect to engine behaviour).


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What could have been done better in United Airlines Flight 232 when differential thrust was used?
In United Airlines Flight 232, on their DC-10, all hydraulic fluid and pressure was lost on all three systems, simultaneously. Fitch, who was a training check airman on the DC-10 was on board and happened to have experimented and practiced using differential thrust on his own time (in the simulator) to see if he could fly the DC-10 just with differential thrust alone.
While I think no one in the world could have done a better job than Fitch in this case (and it seems the rest of the crew misunderstood up to the very last second how differential thrust worked by reading their transcribed comments — telling Fitch to do things that didn't make sense), I'm still curious, what (if anything) could have been done better? Were any reports produced that commented on (I hope also praised) Fitch's effort, and suggested improvements?
In particular, I'm curious what Fitch's plan was. If he hadn't been unlucky at the very last second, when the wing tipped, touching the ground, and the engine was too slow to respond to correct this, what would have happened next? The plane is now on the tarmac and heading down the runway at 220 knots or so. Is there even any stopping power available? I'm sure the brakes also run on hydraulic power, or is this a separate system?
If there is no way to slow down, is it obvious that it is better to let the plane hurdle off the end of the runway, instead of a controlled crash?
I know that differential thrust was attempted in the simulator in the wake of the crash to see if they could establish some differential thrust emergency procedure, but that the pilots who attempted this couldn't even match Fitch's performance.
In any case, is there even anything theoretical to say about this, or is it to this day (this was in 1989) still considered a hopeless situation and death sentence? How do you stop if you even get on the runway?
I'll accept some educated reasoning as a valid answer, and also accept (obviously) links to any official or academic reports that address this.

Brake accumulators can provide several applications of the wheel brakes even with no hydraulic system pressure.

NTSB report for N1819U accident, on July 19, 1989, summarized here. This experience helped in a somehow similar hydraulic failure of a A300 after a missile strike over Baghdad in 2003


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What is the feasibility of converting an F-22 to carrier use?
I read that the Navy originally considered to use the ATF(Advanced Tactical Fighter) Programme aircraft (Now known as the F-22) as carrier aircraft but declined to do so when it came out. How feasible is it now to convert an F-22 to carrier use? (I kind of want to know because it is a better plane than the F-35 but is not used on carriers even though it was originally planed for)

In general, land based aircraft do not lend themselves well to carrier conversion. On the other hand, conversion in opposite direction is (relatively) easy, as shown by F-4 and F-18.
Conversion of aircraft to carrier use require a number of modifications:

Tail hook has to added and rear fuselage reinforced for arrested landings.
Landing gear has to be strengthened for high sink rate (~24 ft/s).
Atleast in USN, the front landing gear and fuselage has to be strengthened for catapult launches.
Also, it requires additional equipment, like th Carrier Landing system, redesigned refueling system (pretty much everyone use a system different from USAF).
Carrier based aircraft usually are expected to have better low speed capabilities as they have to fly slower approaches and wave-off (go-around) at lower speed compared to the land based aircraft. This dictates the wing loading, resulting in increased wing area and/or high lift devices.
There are also issues in corrosion prevention etc.

The weight penalty due to these reasons can be non negligible. For example, the naval Rafale M version weighs nearly 500 kg more than the Air Force Rafale C variant (which has ~10 ton empty weight). USN calculated that the NATF (Naval Advanced Tactical Fighter) will be around 1800 kg heavier than the Air force version (ATF was supposed to weigh ~15 ton).
Another thing is that the USAF and USN had different requirements, for example, the USAF wanting a single seater and USN wanting a double seater, requirement of different sensors (for fleet defence) etc. in the end, the aircraft proposed for the NATF looked nothing similar to the one that finally became the F-22 and the project was quietly buried.

F-22 NATF proposal, image from aerospaceweb.org
Note that the design has swing wings, as the aircraft was being proposed for replacing F-14 Tomcat. Another important result of the navalization of the aircraft is the reduction in the number of planform alignments, and their negative impact on the stealth characteristics.
Carrier conversion of F-22 could have been done if it was considered early in design. Doing it now (note that NATF was considered due to the insistence of Congress; it is doubtful if USN ever wanted it). Doing so later in the design process will result in another F-111B fiasco. As for doing it now, it is better to design a new aircraft (which was what the F-35 is).

Some form of folding wings are also a nice bonus for carrier-based aircraft.

@JörgWMittag As Lockheed's proposal had swing wings, there was no wing folding (like F-14). However, there was a proposal sometime later (not official) which included folding the wings between flaps and ailerons.

Beautiful answer!

One thing to note is that the F-22 is already 50% heavier than the F-35 before any required strengthening or modifications: it's pretty heavy as fighters go

@JonStory although I agree with the given answer's reasoning, keep in mind that the twin F119 engines produce FAR more thrust than the F-35's single Honda V-6... I mean, F135 turbofan. About 30,000 to be exact. If we had another great such as Kelly Johnson, and the funding, AND the government initiative (something I believe has been bureaucratized to extinction in our government) there wouldn't be too much in the way making it happen, disregarding the actual effectiveness of the end result.

"Landing gear has to be strengthened for high sink rate (~24 ft/s)" - Isn't that a requirement even for land-based combat aircraft, given that you're in the middle of a war and can't always guarantee that you'll be able to make a stabilised approach?


text:
How do disks generate lift?
Disks and disk-like objects (frisbees, pie pans, round cardboard piece, hats of all sorts, and many other things) can fly well when thrown along with a spinning force which creates a gyroscopic effect stabilising the object. What causes disk objects to be able to generate lift?

Just the angle of attack. The stability comes from the rotation.

Possible duplicate of How do wings generate lift?

This one should address the topic nicely. A disc has a variable leading edge sweep over span, but works otherwise like a paper airplane. Rotation makes sure that the pitch angle will not change.

One way to view this is that the Frisbie creates drag as is descends. Thus it acts like a parachute.

Why to close this? It is clearly about the list generated by the disk-like flying object and not the paper plane. If this is the same, should be explained. A plane spinning like a thrown disk is unlikely to fly well.

As with regular wings, the angle of attack and the dynamic pressure determine the lift of a frisbee.
This short paper by V. Morrison gives a short overview. If you want to dig deeper, Sarah Hummel and Eugene Motoyama (sorry, paywalled) have done more detailed work on flying discs. The following pictures were shamelessly copied from the work of Kevin Walsh. They show that the rounded edge improves airflow over the disc by delaying flow separation.

Flow around a frisbee (source)
The frisbee can be seen as a wing with an airfoil that looks the same from both directions. This incurs a small separation area at the rear end, but prevents much larger separation at the leading edge at medium angles of attack. Morrison found the farthest flying distances with an angle of attack of 12° and a starting speed of 14 m/s.
Since the center of pressure is close to the leading edge, a disc would quickly topple over due to the different locations of the center of pressure and the center of gravity. By spinning, it can be stabilized:

Difference between spinning and non-spinning frisbee (source). Inertia / gyro forces prevents the spinning frisbee from pitching up.


text:
How can I find the CG of a model aircraft based on its dimensions?
Given the dimensions and gross weight of an RC model aircraft, how can I find the center of gravity? Can I calculate it, or perhaps there's some way to approximate it?

It's impossible just using dimensions because it doesn't give any information as to what is inside the structure, for example the location and size of tanks, the APU, seating, cargo, etc.

Sorry I was asking about CG calculation for a RC model aircraft can we make  assumption from its wing characteristics and its gross weight and engine avionic location to find cg

You can, of course, approximate it by simply finding the point where the aircraft balances.  If your model is small enough, put a broomstick under the plane, parallel to the wings, and figure out how far forward/back to move it to make the plane balance.

What If I don't have the plane just data

What data, exactly, do you have?  If all you have is the dimensions and total weight, then you're out of luck. (Imagine two identically sized, weighted planes, but one has all the weight front-loaded, and the other has all the weight rear-loaded).

I have wing gross weight , root chord ,tip chord , sweep angle , wing span , area and  wing airfoil profile Cl  engine and avionics is the located at the front

Do you know, or can you infer the (relative) density of each component? If you don't, then you can't find the CG, else if the density is constant, the CG is also the centroid of the volume, else you have to compute the barycenter of the mass, based on volume and density. There is no easy method.

Do you mean "find where the CG is now" or "find where the CG ought to be"?

I think it's clear what the question is asking, the answer just happens to be "you can't." And finding CG should be on topic, the fact that it's an RC model is not relevant.

You cannot.
Assuming that by 'dimensions' you mean the values for length, width and height, there is no way to calculate CofG from it. Two planes with exactly the same dimensions, but one with a thicker wings or tail, will have different C of G.
Even if you know the precise shape of the plane, the C of G cannot be calculated. Replacing a wooden tail with a heavier metal one with the same shape would shift the C of G. So would replacing the engine with a heavier one.
You need either the plane itself, or exact plans showing all the components and their weights (and a lot of maths).

The question you have asked is competently answered by DJClayworth.
But I guess you want to ask something different, that is where the center of gravity must be in order to have a well-behaved aircraft. The aerodynamicist's answer would be: Slightly ahead of the neutral point.
First, calculate the areas of both the wing and the horizontal tail. Interpolate between the wing roots to include the section which is covered by the fuselage. These areas are needed for scaling the influence of the wing and the tail.
Next, pick a reference point. The nose of the wing root would be a good choice. Then measure the distance between this reference point and the quarter chord point of both the wing and the horizontal tail. For unswept wings, the quarter chord point of the wing root is sufficient; however, with swept wings you need to find the spanwise station where half of the wing area is inboard.
Use the sketch below for a graphical method: The grey area is the swept wing's planform. First, add one tip chord length at each end of the root chord and vice versa with one root chord length at each end of the tip chord (blue lines). Then connect the ends of the resulting lines (red lines). The spanwise station where they cross is your mean chord (green line). Use the quarter point of this chord (black circle) and carry it over to the root to measure the distance to your reference point.

Do the same for the horizontal tail. If it is a V-tail, use the projected planform in the horizontal plane.
Now all that is left to do is to interpolate the two distances $x_{NP}$ with the respective areas $A$:
$$x_{NP} = \frac{x_{NP_{wing}}\cdot A_{wing} + x_{NP_{horiz. tail}}\cdot A_{horiz. tail}}{A_{wing} + A_{horiz. tail}}$$
Now that you know the neutral point, place the center of gravity at 20% of the mean chord (remember the green line?) ahead of this point. In a normal RC aircraft with unswept wings this is approximately at one third of the chord length from the nose of the wing root chord.

If the model aircraft can actually fly you can narrow down where the center of mass is.
The center of mass will be along the centerline of the aircraft (usually by virtue of symmetry).
When the aircraft is sitting on the ground the CoG will be above the triangle described by the gear. If it has a nose wheel then the CoG will be more towards the rear (so the aircraft can pitch up on takeoff). If it is a tail dragger it'll be more towards the front.
Beyond that the center of mass will most likely be near or just in front of the wing root. That way loss of control will let it remain stable instead.

The type of landing gear a plane has would have no bearing on its CG. The CG would need to remain the same if you switched a plane from tricycle to taildragger gear.

But it helps narrow down where it is. Not to mention that switching gear types requires moving either the main gear or the CoG so the plane can actually sit on the ground correctly.

You can't safely move the cg to accommodate landing gear. That's backward thinking. The cg is a critical component to the flight characteristics of the plane.


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Can a small UAV restart its engine in mid-flight?
Is it possible for a small UAV, say a small piston-engine aircraft with a low windmilling effect, to restart its engine in mid-flight following an engine shutoff?

With most hobby motors, no, this isn't possible. Some larger motors can be made with an electric start but there is no "ignition" like on regular aircraft. Usually the hobby motors stop when the gas runs out/is turned off. They start either by hand propping or by using an electric "starter".

Depends on the aircraft and engine in question.

Some gliders have pop-up engines to extend range if they cant't catch rising air (known as turbo-sustainers) which start by in-flight windmilling, but I wouldn't count on it with an engine not designed to be started this way. Additionally, if the shutoff was not intentional it seems likely that whatever caused the engine to fail will make it even harder to start in this manner.


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Can a jet cruise with asymmetric thrust?
If a twin turbojet aircraft has an engine failure during takeoff, does it return for landing or does it continue to cruise with asymmetric thrust?

As written, you're asking whether an aircraft with only one engine has the option of returning for a landing or continuing. The answer for that, of course, is that the aircraft is going to come down. I suspect what you wanted to ask is whether an aircraft with more than one engine has such an option if one of those engines has failed. If that's the case and you rephrase your question, you might also wish to specify whether the aircraft has two, three, or four engines to begin with as the answer can be different depending on the number of remaining operative engines.

Edited to make things more clear, and specify "twin" engine turbojet to narrow the focus. If this edit does not match not your (kcihtrak's) intent, feel free to roll it back or edit again to reflect your intent.

Related

As a practical matter, the aircraft will probably land ASAP. Having lost an engine pretty clearly qualifies as an emergency for twin-engine aircraft!
That said, the aircraft would be capable of cruising with asymetric thrust. Rudder is applied to keep the aircraft flying straight.

It does not matter whether it qualifies as emergency “pretty clearly”. What matters is that it does by SOP and regulation.

Aircraft are allowed to takeoff in weather conditions that are below landing limits.
So yes, with an engine failure after takeoff, twin engine aircraft may plan a "Takeoff Alternate" up to one hour flight time away.
In cruise, modern twin jet airliners like the B777 and A330 are designed to fly ETOPS ("Extended-range Twin-engine Operational Performance Standards") for up to 330 minutes engine to a suitable landing field on ONE engine.

ETOPS don't, however, permit passing on a good alternate, does it? That is, you still must land ASAP, it just might happen that you are flying a route where nearest diversion field is 330 minutes away.

The jet will take off, but declare an urgent situation and either land as soon as practical if the aircraft is below gross landing weight or be directed to a holding area to either dump off or burn off fuel until the a/c is below gross landing weight, and then land as soon as practical.

Not always.  747s (and possibly other types, I just happen to know that 747s have done this) have been known to carry a "dead engine" on a return journey and have taken off with an inoperative engine and some have lost an engine in flight and continued to their destination.

@Simon: Sorry - I came late to the party.

On the other hand, twin must declare emergency, which is rather different thing from “urgency”. And emergency generally means land ASAP, overweight or not.


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When one engine fails in a twin-turbojet aircraft, is there a weight imbalance?
In a turbojet aircraft with two engines, when one fails does the weight of the working engine increase due to the fuel flowing to it? If it does, how is the weight balanced on the failed engine side?

Even if the weight were to increase in relation to the failed side (which it really doesn't), it would be insignificant. The actual weight of the fuel in each engine, even large ones, is probably less than 50lbs. The failed engine would still have fuel in its system (unless it was a fuel leak or fire), so it probably wouldn't change. The biggest issue is asymmetrical thrust.

Only if the failure was caused by the engine falling off the plane. Otherwise no.

for turbo prop and turbo fun engine failure your are supposed to balance your plane using ailerons and rudder

The engine can't contain more fuel, because the pipes don't expand and the fuel does not compress. Higher fuel flow just means the fuel moves through the engine faster, but there is still the same mass of it at any given moment.

Since your question is specifically on "jets".
We need not worry about the critical engine.
There is one thing to be noted in most of the commercial jets. The engines are placed close to the fuselage in order to reduce the moment arm - mean that should an engine fail, there is a reduced difference in forces,as compared to if an aircraft had engines on the wings tips.
The following are two vital things to be carried out during imbalance due to engine failure:
1) Effective rudder (and aileron) control:
The rudder (and aileron) is used to maintain directional control in flight, acting around the normal axis. An engine failure will yaw (and roll) an aircraft, making the rudder (and aileron) the best control to counteract this.
2)Fuel Balance procedure:
The following procedure is for a Boeing 737 :

Detailed schematic of a B737 Fuel System:

The procedures vary from one aircraft to another. And for a turbo prop aircraft it's a whole new thing involving "critical engine".

Fuel systems are designed such that when an engine fails, fuel is no longer supplied to that engine. Further, fuel can be supplied from the tanks(s) on the failed side to the operating side to maintain balance as the operating engine continues to burn fuel. The details of how this is done and the extent to which it is automated depends on the aircraft type.


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What will happen if satellite navigation fails?
My understanding is that aircraft use GPS systems for navigation (maybe not the only way to navigate). I would like to understand what would happen if the GPS system fails.  Are there any other navigation systems to fall back on? What would happen if all of them fail? Could all the navigation systems fail?

Many other navigation systems exists. Here is a (perhaps non exhaustive) list

Airliners were commonplace long before GPS was. GPS only became fully operational in 1995.

All of these answers seem to wholly ignore the situation where you're out above the middle of an ocean?  Of course, obviously, it's incredibly unlikely all gps/glonass satellites could "break down", but there are any number of obvious ways (starting with "simple bug" and "political situation") where both systems could go completely dark.  Is this theoretical situation tough, if you're halfway across the Atlantic or halfway to Australia?

Also FTR to interpret the question well, of course all your on-board GPS systems could fail: say you have three or four GPS on a plane, it's totally reasonable to consider them all failing - battery woes, whatever ... sure, it's unrealistic that all the satellites would fail

No matter where you are, even in the middle of the ocean, maintaining a fixed compass course for a set amount of time will always get you reasonably close to your destination.  You may be off course a little due to crosswind errors.   But you should still be able to find the right coastline!

@JoeBlow INS deals with the halfway across the Atlantic scenario.

cool ... interesting

@abelenky It is possible to memorize the route if its short distance and the pilot has flown this route 1,000 times so it is possible

@Ethan:  That is NOT what your original message stated.  Memorization is clearly possible.  But you wrote that, absent memorization, navigation would be impossible.  That is obviously not true.  Navigation without memorization is actually pretty easy.

As a note for dealing with the unrealistic aspect of satellite navigation systems failing: there is no known navigation system which does not have the potential for failure, so it could theoretically happen.  All navigation systems to date cease to function when they plow into the side of a mountain.  Fortunately, by the time this occurs, you are usually not majorly affected by the lack of navigation.

planes don't use GPS

@JamesRyan: Do you want to explain that comment?  Planes, auto pilots and human pilots all definitely use GPS.  That is what an "RNAV" approach is.   Perhaps you mean that not all planes use GPS?

@abelenky by that I mean that it is convenience only, it is not used for plotting courses or avoidance.

Again: Flat wrong.  To perform an RNAV approach, GPS is 100% required.  I believe there are certain STARs and DPs that also require GPS.  (I'm not IFR rated, I might be wrong on that last part)

It only takes 3 satellites for a GPS fix (4 if you want altitude). There are 31 operational satellites currently in orbit and at any given time you can most likely receive a signal from half a dozen of them at least. That being said the chances of them failing completely is almost 0%. But of course what if they did, well...

There is always the Russian version of GPS known as GLONASS so there is effectually an entire redundant global navigation system in space. While not all aircraft are equipped with GLONASS receivers it is of course becoming more common. Even the little tiny receiver I use for GA flights has it now. So there is that redundancy.

In controlled airspace you have ATC there to help you. They can effectively watch you on radar and tell you what to do which is basically what flying IFR is. For this you will need an operational altitude encoding transmitter so that ATC knows your altitude along with position. If you are flying VFR and require assistance you could call for Flight Following here in the US, load permitting. They can offer limited guidance but if you tell them you are lost they will generally help.
If there is no ATC you can hone in on VOR stations, or some of the older radio direction finders like ADF systems assuming your aircraft is equipped with such equipment. Some modern handheld radios can also hone in on VOR stations

If all that fails you have your good old magnetic compass and hopefully some way of keeping time. With close track of your airspeed, a clock, and a compass you can navigate pretty accurately even in the blind (although I don't recommend that).

No compass, no problem, you always have your ground reference points to get where you need to be. Basic VFR navigation which every pilot know how to do is learned this way. This will require you have a VFR map of the area which most GA planes will carry. Note the roads, power lines and other large things marked on the map that are easily identified from the sky.

Outdated/less popular systems:
Inertial navigation systems are still used in plenty of places however they are not as accurate as other systems available in modern aircraft but they work by knowing how fast you have gone and in what direction you have accelerated to that speed. Thus position can be calculated. INS systems suffer from integration drift which can add up over time and make the margin of error pretty big.
There was once a time in history when you could get a navigators rating on your license. These people were trained in many times of navigation including celestial navigation. Older planes were even outfitted with a sextant for that very reason.

LORAN C was officially shut down here in the US/Canada in 2010 but there are still active chains elsewhere in the world. Some planes out there still have the units in them (one of the Cherokees I fly still has it sitting there). So depending on where you are you may be able to use it.
What Time Is It:
The US GPS network is synced up via the USNO master clock and while it is unlikely that all the satellites will fail simultaneously or fall out of the sky, or be shut down. The master clock does provide a central point of failure for the system. While I am not up to date on the full function of the system I would imagine that a downed clock could introduce a margin of error into the system. Worse so an incorrect value fed from the master system may cause an erroneous reading.

Certified aviation GPS receivers need a minimum of 5 satellites (for RAIM)

It's nice that the Russians use pretty colours!  :)

what is Flight Following?

see here http://www.avweb.com/news/avtraining/183268-1.html

Well, the point is that if a war began, maybe someone would instantly shut down or shoot down GPS satellites, so it could happen that they become unreachable suddenly.

True. The government also has the option to degrade civilian use of GPS in several ways, without compromising military use. It can reintroduce selective availability which would make all civilian GPS only accurate to about 150 feet, and it also has regional denial capabilities that allow EW aircraft or the satellites themselves to obfuscate the coarse acquisition signal, possibly in a way that friendly aircraft can de-obfuscate using a key of some sort.

Actually, GPS is not as reliable as everyone seems to believe. All it takes is a solar flare, or a 10W jammer from eBay. This is not at all an unlikely scenario.

INS is essential in modern aircraft. Aircraft generally don't use GPS directly, they use it to compensate drift of the INS and use data of that for all instrumentation, which in integrated glass cockpit packages includes attitude indicators, gyrocompass and autopilot and in fly-by-wire aircraft the flight envelope protections and the cooked commands. Because INS can provide the necessary 100 or more updates per second while GPS has only one per second.

Plus of course the point of INS is that if GPS fails the INS will still be pretty good. It will start to drift, but it can still give you e.g. 8 minutes of RNP 0.3 and 25 minutes of RNP 1.0, so you can safely abort the RNP approach and fly to the alternate which has better weather or good old ILS.

@KeithS:  Selective Availability could technically be turned on, but doing so would be in violation of the executive order that shut it off.  It wouldn't do a great deal anyway since the Block IIF satellites are incapable of SA.  The first of those was launched in 2010 and the last of the 12 planned should be in service next summer, by which time a third of the entire fleet will be SA-incapable.

@Birfl - All true. Executive orders are fairly easy to rescind, though, and 2/3 of the system being unavailable for enemy use, depending on the dispersion of Block IIF satellites within the constellation, might well make the system unusable for precision navigation in the right areas. Of course, most of our enemies would then simply turn to GLONASS unless that same enemy happened to have pissed off the Russians too.

And if all of those things fail, the price of LORAN-C receivers on eBay will go up and someone will try to figure out how to dust off the transmitters. :)

Thanks everyone for these interesting answers and comments. I am delighted!!!

Shoutout for the Galileo system which should be a counterpart to GPS and GLONASS, someday.

GPS is not limited to 1Hz, even if most consumer units are only 1Hz receivers.

It's worth noting that aircraft routinely rely on INS for navigation, particularly when flying polar routes. Once you are inside the arctic circle, GPS navigation becomes somewhat unreliable, and as such only aircraft with self contained navigation systems are certified to fly polar routes. Also, as mentioned, GPS only became available in 1995. There are still a lot of planes flying that were built/designed prior to 1995.

re: "the chances of them failing completely is almost 0%" – the military can disrupt GPS, see the article in https://aviation.stackexchange.com/questions/57035/how-to-navigate-an-aircraft-without-gps

You need four satellites for a GPS fix, not three; the fourth is to allow the receiver to calculate how inaccurate its internal clock is and compensate for that.

The probability of the entire GPS system to fail is quite low. Individual satellites may fail, however that can be detected by the GPS receiver itself. Usually there are more satellites in view than minimally needed so the faulty satellite will be excluded from the position calculations.
If no GPS position can be calculated, for example because of a failure of the GPS receiver, the aircraft has a number of alternative navigation systems.
In no case GPS will be used as the sole means of navigation. There are always other navigation systems used in parallel.
Aircraft are equipped with VOR receivers, which uses signals from ground based navigation beacons to determine their direction. These VOR stations have a range of up to 200 NM. This isn't of much use of the oceans of course.
Inertial Navigation Systems calculate the position by keeping track of all accelerations and rotations of the aircraft. The accuracy degrades over time but it is good enough to find your way over the oceans. The good thing about INS is that it is totally independent of external systems.

The probably of it failing might be low, the probability of someone itching to push the button and turn it into US military use only might be a bit higher... :)

Actually, GPS is not as reliable as everyone seems to believe. All it takes is a solar flare, or a 10W jammer from eBay. Doesn't mean the satellites themselves are "broken", but even if we're not talking about an interferer local to the receiver, there can be enough uncertainty between the ground segment and the satellites to reduce overall effectiveness and cause problems for critical missions. You need redundancy (in this case, tried and tested human navigation skills suffice). This is not at all an unlikely scenario.

If your GPS receiver (or the entire GPS system) fails, what you have left depends on what you have to begin with. Many GA aircraft that have been upgraded with a GPS receiver (and quite a few that came stock will full glass) still also have a good old navigation radio stack with at least one Omni Bearing Indicator:

This indicator works with a radionavigation system called VOR (VHF Omnidirectional Range). Ground stations at known locations broadcast a two-part signal; an omnidirectional radio beacon that identifies the station, and a sweeping, phase-shifting transmission of the same modulated signal that the nav radio compares with the omni signal. The amount of phase difference between the omni and sweeping signal is the same as the compass direction or radial from the station to the plane.
Pilots can use this system to fly "Victor routes" between major cities by selecting the VOR radio station they want to fly toward or away from, then dialing in the desired radial they want to approach along (which may be important to avoid obstacles or restricted/controlled airspace), then flying diagonally to that course to intercept the radial before turning toward or away from the station As they approach or pass one station, they can tune in to the next VOR station and radial indicated on the chart.
Using two radios, they can also triangulate their location based on the readings from two VOR stations; fly along one radial until you intercept another radial of a different station, and now you know you're at the intersection of those two radials on the map.
VOR (and other radionavigation methods like the military equivalent TACAN) are not quite as accurate as GPS, nor quite as reliable in all scenarios (many of these systems require line of sight which is more difficult in mountainous terrain or at very low altitude) but it's been the system that U.S. civil aviation has depended on since the 1960s, and if you know how to use it properly it works quite well.

A fail of the GPS system wouldn't cause any issue to properly trained pilots. Remember that aviation started in the early twentieth century! However if you have no visibility and all the navigation systems (or, more probably, just the pilots) fail, then you are in trouble and you can eventually crash. Just a couple of examples from the top of my head:

If you get completely lost at night in the middle of the Amazon forest you will probably run out of fuel and crash (see Varig Flight 254).
If you think that your navigation system is guiding the plane while it's accidentally off, you may end up on a nearby hill instead of the runway (see First Air Flight 6560 - note that even the GPS was working correctly but the pilots were confused).

In modern aircraft, this would happen (FMC intern uses these on priority basis 1. GPS 2. DME 3. VOR 4. IRS). In old aircraft their order remains same without FMS in place.
https://en.wikipedia.org/wiki/Flight_management_system#Position_determination

There's a bunch of alternatives for the case that GPS fails. I guess that they would first resort to VOR-navigation ( http://www.pyrochta.ch/flash/start_vor.htm ). And if all else fails you'd still have a compass, a map and a clock for timing.
But I think that, if all communication failed as well, at some point some fighters would guide you to the next airport.
You will be never in a situation where you don't know anymore where you are and where you're going.


text:
Who decides how to "handle" an aircraft, with regards to severity of manoeuvres etc?
Until Friday I'd flown only with EasyJet and Alitalia. In the last weekend, however, I took two Vueling flights and felt that the way the aircraft manoeuvred during the flight was very different when compared to EasyJet and Alitalia.

Take off seemed more "brutal", and we seemed to rotate much earlier, where the EasyJet or Alitalia flights will use more of the runway.
After take off, the airplanes did a lot of maneuvers during climbing. While EasyJet's planes usually do a variation of "turn, long climb, another turn", the Vuelings' performed a number of turns during climbing.
Landings, from the point of view of turning, are the same (as it should be). But after touchdown...it seemed to me the pilot maintained a higher rollout and taxi speed for much much more time, so that in both cases after the gear touching ground the plane reached the apron in a matter of seconds - and in both case the planes were yawing a lot when completing their landing roll and taxi, compared to the EasyJet or Alitalia flights.

In general the impression was that pilots were piloting in a more "sporty" manner (to use a motoring analogy), if you'll allow me the expression, and other passengers noticed it too.
So, question is: was it really just an impression? And if not, is there some kind of "direction" the airlines give to their pilots in how handle the plane?
Notes:

I'm NOT criticizing in any way the pilots. I know standards are
pretty high and is not the kind of job one can improvise or do
careless; I'm not saying or implying that they did pilot badly.
Airplanes are pretty the same, I've flown with EJ's A319 and A320,
both with winglet fences, and the Vueling's one was a brand new A320
with sharklets.
Air conditions were not extreme. In fact, I usually fly
Easyjet in winter in north Europe (MXP/LGW/CDG) in bad weather
conditions, while the Vueling flights were during clear days between MXP
and BCN.

P.S. notice that, as I'm not an English native, I had difficulties to post a question in a good format for the site. Please anybody feel free to edit it for improvements, but the note about this is not a criticism against pilots has to remain. Thx

Did you fly another airline on the same route or a different one.

@JanHudec That might explain a lot, but it might not explain everything.  Terry and casey (both were ATP, for anyone who may not know) have both commented that different carrier train their pilots differently, and that airlines have different procedures for aircraft maneuvers at times.  Granted, I was under the impression that it was mostly for little things, so I doubt that would fully explain all the differences between the flights mentioned.

@JayCarr, hm, why don't I see those comments...

@JanHudec lol, on other questions and in the chat room, that's where I heard those comments.  Casey has talked about training in the chat room on a few occasions.  And there's an answer around here somewhere where Terry talks about how different carriers would have him use different procedures to do a take off in the 747-200 he flew.  Granted, he had learned somewhere else so he ignore the procedures he didn't like...but I think a new guy wouldn't have known the difference.

@JanHudec Remember, I don't think this would explain all the differences the OP is describing (weather, terrain and traffic patterns clearly make more sense.)  But different carriers do train differently, so that may contribute just a bit.

Different carries may also have different SOPs, e.g. minimise taxi time; and ops schedules, e.g. quicker turnarounds so less time on ground.

Thx, Jon. Where/were is a mistake I make too often, and for the rest...I always like to be corrected, so I can improve :-)

Just wanted to point out a thing: while passengers around me noticed the more aggressive style of piloting, it was not something like the pilot doing tonneau or Immelmans during landing or such. I did notice a few minor things, nothing really radical.

An Immelman during landing would be very impressive!

The departure path for BCN runway 25L requires a prompt turn to the left for environmental reasons. Maybe this was the reason for the "brutal" takeoff.

Pilot in command, a.k.a. captain, has the last say in how the aircraft will be handled. However most of their decisions are driven by something:

Obviously performance of the aircraft. This is affected by weight (both cargo and fuel; aircraft only take the amount of fuel they need for the route they are flying and it makes a big difference) and weather (mainly temperature and head-wind).
Standard operating procedures (SOP). Certain operations can indeed be done in more than one way and each airline may indeed make slightly different choices. These are reflected in the recurrent pilot training.
Route flown. Airline flights are carried out under instrument flight rules, so the route is assigned by the air traffic control.

Take off seemed more "brutal", and from a position slightly more at the beginning of the runways.

There is some freedom in choosing the take-off setting and standard operating procedure of different airlines may make different choices. Usually if the runway is long enough the engines are not set to full thrust, but so called “flex” thrust that is calculated sufficient for the take-off to limit wear of the engines.
What thrust and flap setting are possible is determined by weight, runway length, wind and temperature, but within the possible range, different airline may have different preference in their SOP (higher power or less flaps for faster climb v.s. lower power for less engine wear and more flaps for lower gear wear).
Noticeable difference might be in using “rolling take-off” where power is added immediately after turning on the runway without stopping there first. Whether it is possible depends on ATC, but some airlines seem to never do it.

After take off, the airplanes did a lot of maneuvers during climbing. While EasyJet's planes usually do a variation of "turn, long climb, another turn", the Vuelings' did "a lot" of turns during climbing.

This depends on the departure route assigned by the controller. Note that even if flying the same route, the departure route could be different if different runway was used or if different routing was selected due to congestion (European airspace gets very busy at times and then the plane may wait or use different route).

Landings, from the point of view of turning, are the same (as it should be).

Not necessarily. Arrival routes may differ similarly to how departure routes do. In fact even more so, because on arrival the aircraft are often vectored, that is get ad-hoc headings assigned by controller instead of flying standard route depicted on the chart, to achieve appropriate separation. On take-off the aircraft simply wait on the ground until the previous aircraft is far enough so it's not needed often.

But after touchdown...it seemed to me the pilot kept an higher speed for much much more time, so that in both cases after the gear touching ground the plane reached the apron in a matter of seconds

Again there can be differences in SOP regarding preferred auto-brake setting, but usually every pilot will want to vacate the runway as soon as possible, so it seems more like difference in what exits were available.
It might have also been difference in the aircraft. There was some talk about Airbus implementing “brake to vacate”, where the computer handles the brakes so the aircraft slows down just before the next suitable turn-off, on the new A320, but I found no reference whether they already did.

and in both case the planes were swinging a lot.

The vertical tail acts like a weather-vane and the thrust reversers reduce lateral stability, so the aircraft always needs some directional corrections during landing.
In the air the aircraft turns by banking, so you don't feel any lateral movement. But on the ground it can't and due to the speed you feel even very slight turns.

Whoever is pilot in command decides how to fly the plane. Commercial airlines have professional instructors who examine the more junior pilots and give them guidance on how to fly smoothly. In general, pilots with passengers try to avoid flying in a way that would make them uncomfortable. However, it is completely up to the pilot at the end of the day.
If a particular pilot or crew generate a lot of passenger complaints, the airline might warn the pilots or even fire them.
Note that different flights will have very different maneovering requirements depending on the flight path. So, even if you take the exact same flight multiple times, factors like wind direction and traffic can result in much different amounts of maneovering during ascent and landing.


text:
In an F-16, at what altitude is supplemental oxygen considered essential life support?
Combat aircraft like the F-16 employs hypobaric pressurisation with supplemental oxygen from a regulator.
However, at what point does the manual call for the pilot to start using the regulator, what altitude?
As a bonus:
What is the maximum altitude one can sustain flight with only hypobaric pressurization under normal operation? Can the pilot fly at say, 20 thousand feet, without ever needing to care about the regulator?
My own reasoning:
It is possible to ascend Mount Everest (approximately 30 thousand feet) without oxygen. Obviously not everyone can do this, but, for a limited time, it seems plausible that the sheer altitude wouldn't be fatal. However, I imagine the manual calls for the regulator a lot earlier than when it becomes dangerous to not have it, for practical and safety reasons. I just have no idea when that point would be, perhaps the manual always states to have the regulator on, that would be the safest option.
Bonus part:
Again, I don't know.
The hypobaric pressurization alone would alleviate somewhat the need for supplemental oxygen, so perhaps it is possible to survive, although not comfortably so, beyond 30 thousand feet for multiple hours, thanks to the pressurization.

The cabin of the F-16 airplane is pressurized via bleed air from the engine, which provides bleed air for this, environmental control and anti-G systems.  See the schematics below.

The pressurization schedule is automatically controlled according to the chart shown below.

Onboard oxygen for breathing is provided by a liquid oxygen system controlled by an oxygen regulator.  See schematic below.

This is a diluter demand oxygen regulator which also provides pressure demand modes for cabin altitudes above 30,000 ft as well as for anti G enhancement.  As the oxygen mask is typically worn during all phases of operation, the regulator would be in use throughout this.
As for oxygen requirements, the military has similar ones to civil aviation.  Pilots need to be using oxygen at cabin altitudes above 14,000 ft at all times in order to remain fully alert with all cognitive functions intact for flight ops and combat.
And, in regards to your comments about climbing to the top of Mount Everest, no, human beings cannot survive up there for extended periods of time without supplemental oxygen.  People who have scaled Everest without using oxygen have

Been in exquisite physical condition prior to making the ascent
have acclimated themselves to higher altitudes at the base camps and
expedite the ascent to the summit and return below 26,000 ft.

Pressurization to a particular cabin altitude creates a breathing environment identical to actually being at that altitude.  For example if you are cruising in an airliner at 35,000 feet with a cabin altitude of 7,000 feet this is no different than being on top of a 7,000 foot mountain, other than the difference in temperature and humidity.
As shown in the chart in one of the other answers the F-16 pressurization system can operate with a pressure differential of 5.0 psi. This means that at an altitude of 23,000 feet you would have a cabin altitude of 8,000 feet, which is the maximum cabin altitude allowed in airline operation because of the wide ranges in medical conditions of airline passengers. At 26,500 feet you would have a cabin altitude of 10,000 feet, which is generally considered a safe unpressurized altitude for pilots. At 34,000 feet you would have a cabin altitude of 14,000 feet, which is the maximum allowed for general aviation pilots. And yes someone who is an experienced mountain climber who is aware of their physical limits could probably go higher, they could for example fly at 44,000 feet which would have a cabin altitude of 18,000 feet.
However this doesn’t mean that it’s safe for fighter pilots to doff their oxygen masks during flight, for multiple reasons. High g-force maneuvers make it harder to breath, the positive pressure that is provided by oxygen masks can help with this.  Oxygen masks are also needed when ejecting, and there may not always be time to put the mask back on in time.  Also a cabin leak in a fighter jet will possibly lead to a much more rapid depressurization than would typically occur in a much larger aircraft cabin. Again there might not be enough time to put on the oxygen mask or descend to a lower altitude prior to losing consciousness.
The reason that airliners can cruise at 40,000 feet or higher and still maintain an 8,000 foot cabin altitude is because they have a higher pressure differential limit on the airframe, typically between 8 and 9 psi. Concorde notably had a maximum differential of 10.7 psi, which allowed it to maintain a cabin altitude of 6,000 feet at its service ceiling of 60,000 feet.


text:
What are the major causes of flameout, excluding ingestion of foreign objects?
What are the most frequent causes of flameout, excluding ingestion of foreign objects and other sudden forms of damage to the engine?
I'm limiting this to modern turbojet and turbofan engines with a computerized (digital), closed loop engine management system.
E.g. what could cause a F119-PW-100 engine to flameout or otherwise fail?
I'm not looking for a thorough study or carefully detailed statistics, I doubt something like that even exists. I'm basically asking if this ever happens, or if this is basically a thing of the past with early fighters, such as the Me 262. Are modern jet engines "bulletproof"?
If it does happen, then how?

Fuel exhaustion usually does the trick.

@Ron Beyer Right, but that would probably be one of the cases I'm not looking for. E.g. I believe I've heard that during certain angles of attack on certain combat aircraft, it is possible for the engines to flameout.

You might be counting this as FOD, but I'm going to go with water.  That is, more rain volume than the engine can handle.  It's the reason you select continuous ignition while in moderate to heavy rain because the chance of flameout is quite high.
Next in line would be flow disturbances at very high altitude, that are normally tolerable at low altitude.  Airliners that have gotten into high altitude stall incidents can flame out one or more, especially airplanes with tail mounted engines that are in the wing's down wash.
On some airplanes the stall protection system will activate continuous ignition automatically when you are close to or at stick shaker.  Modern FADEC engines usually have an auto-relight function built in and have to demonstrate auto-relight capability for certification.
Fighters like the 262 and other first generation engines had a fuel control system that was basically a needle valve connected to the thrust lever. The pilot's eyes and brain was the real fuel control and the gauges had to be monitored carefully when making power changes.
In the early 50s hydro pneumatic fuel controllers allowed "slam acceleration" without flaming out, but engines were still sensitive to flow disruptions.  Then  variable guide vanes came along to manage the flow through the axial compressor to control blade angle of attack, and flame outs due to flow disruptions only occurred with more extreme conditions.

I'm not the downvoter so I'm curious: is the downvote because there's a mistake in this answer? Let us know!

I don't see a downvote...

Damn I must be too used to Reddit where all comments are +1 initially. Anyway, here's yours!